The present invention relates generally to electrostatic actuators and more particularly to rotary electrostatic microactuators with comb drive assemblies.
Many early rotating electrostatic motors used a central bearing with various arrangements of electrostatic stators around the motors to effect rotation. Unfortunately, these motors tended to have problems with friction at the central bearing and have had lifetime issues related to wear of the bearing. The motors typically acted as stepper motors where the rotor rotates with an incremental motion as the stator elements are attracted. Thus it was difficult to precisely adjust a plate to a particular angle with such motors.
Other angular motors have been described which use flexural elements to support a rotating element. Comb drive fingers are arranged in concentric arcs around a central flexural pivot, so that small angular motion is provided around the pivot. See, for example, D. A. Horsley, et al., xe2x80x9cAngular Micropositioner for Disk Drivesxe2x80x9d, Proceedings of the Tenth International Workshop on Micro Electro Mechanical Systems, 1997, pp 454-458; L.-S. Fan, et al., xe2x80x9cBatch-Fabricated Area-Efficient Milli-Actuatorsxe2x80x9d, Proceedings 1994 Solid State Sensor and Actuator Workshop, Hilton Head, pp 38-42; T. Juneau, et al., xe2x80x9cDual Axis Operation of a Micromachined Rate Gyroscopexe2x80x9d, Proceedings 1997 International Conference on Solid State Sensors and Actuators, V.2, pp 883-890; E. H. Klaassen, et al., xe2x80x9cSilicon Fusion Bonding and Deep Reactive Ion Etching; A New Technology for Microstructuresxe2x80x9d, The 8th International Conference on Solid-State Sensors and Actuators, and Eurosensors IX, Stockholm, Sweden, Jun. 25-29, 1995, pp 556-559; W. C. Tang, et al., xe2x80x9cLaterally Driven Polysilicon Resonant Microstructuresxe2x80x9d, Sensors Actuators 20, 1989, pp 25-31 (IEEE reprint pp. 53-59) and U.S. Pat. No. 5,025,346 to Tang et al. Unfortunately, all of these devices provide a limited angular range of motion.
In general, it is an object of the present invention to provide a rotary electrostatic microactuator with an improved range of angular motion.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character in which side instability forces in the one or more comb drive assemblies of the microactuator are minimized.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character which permits rotation of a member extending out of the plane of the microactuator.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character which is other than circular in shape.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character in which the axis of rotation of the microactuator is disposed adjacent a side of the microactuator.
The present invention provides a rotary electrostatic microactuator that includes a substantially planar substrate and a rotatable member overlying the substrate for rotation about an axis of rotation extending perpendicular to the planar substrate. First and second spaced-apart springs and a plurality of comb drive assemblies are included. Each of the comb drive assemblies has a first comb drive member mounted on the substrate and a second comb drive member. Each of the first and second comb drive members are provided with arcuate comb drive fingers. Each of the first and second springs has a first end portion secured to the substrate and a second end portion secured to at least one of the second comb drive members for suspending the second comb drive members and the rotatable member over the substrate. The second comb drive members are movable in a direction of travel about the axis of rotation between a first position in which the comb drive fingers of the first and second comb drive members are not substantially fully interdigitated and a second position in which the comb drive fingers of the first and second comb drive members are substantially fully interdigitated. The plurality of comb drive assemblies can optionally subtend an angle of approximately 180xc2x0 about the axis of rotation to form a semicircle having abase extending substantially along a diameter of the semicircle with the axis of rotation being disposed adjacent the base at the center of the semicircle. Alternatively, the microactuator can be substantially circular in shape. The first and second springs can optionally be folded. In another aspect of the invention, a push-pull rotary electrostatic microactuator is provided.